Numerous hydrocarbon conversion processes are widely used to alter the structure or properties of hydrocarbon streams. Such processes include isomerization from straight chain paraffinic or olefinic hydrocarbons to more highly branched hydrocarbons, dehydrogenation for producing olefinic or aromatic compounds, reforming to produce aromatics and motor fuels, alkylation to produce commodity chemicals and motor fuels, transalkylation, and others.
Many such processes use catalysts to promote hydrocarbon conversion reactions. These catalysts tend to deactivate for a variety of reasons, including the deposition of carbonaceous material or coke upon the catalyst, sintering or agglomeration or poisoning of catalytic metals on the catalyst, and/or loss of catalytic metal promoters such as halogens. Consequently, these catalysts are typically reactivated in a process called regeneration.
Reactivation can include, for example, removing coke from the catalyst by burning, redispersing catalytic metals such as platinum on the catalyst, oxidizing such catalytic metals, reducing such catalytic metals, replenishing catalytic promoters such as chloride on the catalyst, and drying the catalyst. For example, U.S. Pat. No. 6,153,091 discloses a method for regenerating spent catalyst.
In a some regeneration processes, a catalyst is passed from a hydrocarbon reaction zone (reaction zone) to a catalyst regeneration zone which may include a burn zone, a chlorination zone, a catalyst drying zone, and a catalyst cooling zone. The catalyst includes coke, which is burned off from the catalyst in the burn zone. A chloride, which is a catalytic promoter, is replaced on the catalyst in the chlorination zone. The catalyst is dried in the catalyst drying zone, and cooled in the catalyst cooling zone, and then returned to the reaction zone.
In the chlorination zone, a chlorine-containing species (chloro-species) typically is introduced to contact the catalyst and replenish the chloride. The chloro-species may be chemically or physically sorbed onto the catalyst as chloride or may remain dispersed in a stream that contacts the catalyst. However, the introduced chloro-species causes a flue gas stream vented from the regeneration zone, referred to herein as regeneration vent gas, to contain hydrogen chloride (HCl). Emissions of HCl in the regeneration vent gas pose environmental concerns if the regeneration vent gas is purged to atmosphere.
Vapor phase adsorbent processes for removing HCl, such as those described in U.S. Pat. No. 5,837,636, significantly reduce regeneration vent gas HCl emissions without the need for caustic scrubbing. An example HCl adsorption process cools the regeneration vent gas. The cooled regeneration vent gas is contacted with spent catalyst in an adsorption zone where HCl is adsorbed onto the catalyst. The vent gas product from the adsorption zone is depleted in HCl and vented to atmosphere or routed to further downstream processing.
This adsorption zone is conventionally integrated into an existing regeneration zone by retrofitting the adsorption zone into a disengaging hopper through which spent catalyst is introduced into the regeneration zone (typically a vessel). However, such retrofitting in certain cases can be difficult to implement to optimize the performance, operability, and/or maintainability of the adsorption process. Further, retrofitting typically requires significant modification or replacement of the disengaging hopper, which is performed during a unit shutdown, increasing costs.
Therefore, there remains a need for effective and efficient processes for adsorbing HCl from a regeneration vent gas.